Orexin-A inhibits fictive air breathing responses to respiratory stimuli in the bullfrog tadpole (Lithobates catesbeianus) [RESEARCH ARTICLE]

Elisa M. Fonseca, Tara A. Janes, Stephanie Fournier, Luciane H. Gargaglioni, and Richard Kinkead In pre-metamorphic tadpoles, the neural network generating lung ventilation is present but actively inhibited; the mechanisms leading to the onset of air breathing are not well understood. Orexin (ORX) is a hypothalamic neuropeptide that regulates several homeostatic functions, including breathing. While ORX has limited effects on breathing at rest, it potentiates reflexive responses to respiratory stimuli mainly via ORX receptor 1 (OX1Rs). Here, we tested the hypothesis that OXR1 facilitate the expression of the motor command associated with air breathing in pre-metamorphic bullfrog tadpoles (Lithobates catesbeianus). To do so, we used an isolated diencephalic-brainstem preparation to determine the contributions of OX1Rs to respiratory motor output during baseline breathing, hypercapnia, and hypoxia. A selective OX1R antagonist (SB-334867; 5 – 25 µM) or agonist (ORX-A; 200 nM-1 µM) was added to the superfusion media. Experiments were performed under basal conditions (media equilibrated with 98.2% O2+1.8% CO2), hypercapnia (5% CO2) or hypoxia (5-7% O2). Under resting conditions gill, but not lung, motor output was enhanced by the OX1R antagonist and ORX-A. Hypercapnia alone did not stimulate respiratory motor output, but its combination with SB-334867 increased lung burst frequency and amplitude, lung burst episodes, and the number of bursts/episode. Hypoxia alon...
Source: Journal of Experimental Biology - Category: Biology Authors: Tags: RESEARCH ARTICLE Source Type: research